A growing body of research is pinpointing the surgeons most likely to cause harm or death during operations, creating powerful benchmarks for obtaining safer medical care. A simple question posed to surgeons, the research shows, can often separate the talented from the average: How often do you do this?

The work builds on earlier research that established that busy hospitals generally deliver better care. But it adds a new level of precision, citing the specific risks patients face in the hands of low-volume surgeons, who don't frequently and regularly perform certain procedures.

These surgeons become most dangerous, the studies found, during AIDS treatments, carotid artery blockage surgery, pediatric heart surgery, as well as surgeries for cancers of the lung, pancreas, esophagus, rectum, and prostate. These are complex procedures, often requiring precise cuts and scrapes near the nerves and arteries of gravely ill patients.

One study estimated that up to 13 out of every 100 surgical deaths in these procedures could have been prevented in the hands of high-volume surgeons. Other studies have shown slightly smaller risks from low-volume surgeons during coronary artery bypasses, coronary angioplasties, and some orthopedic procedures.

Health specialists said the new data, collected mostly in the last three years, should encourage patients with these afflictions to exercise extra vigilance when selecting surgeons. On the other hand, they can probably ignore the more casual selection criteria patients often resort to, such as medical school, research track record, years of experience, or word of mouth reputation.

"It is now a very legitimate question to ask a surgeon: How much experience with a procedure do you have? What are your complication rates?" said Tufts-New England Medical Center's surgeon-in-chief, Dr. William Mackey. "It's something every surgeon should keep track of and show patients if requested."

Most surgeons and hospitals should disclose volume and complication rates for specific procedures to inquiring patients, said health specialists. Hospitals typically do not force them to share the information, though almost all surgeons keep track of patient volume through billing records, with most also logging complications.

Studies have shown that low-volume hospitals and surgeons are not usually in sparsely populated rural areas, as might be expected, but just outside hospital-filled metropolitan areas, such as Boston, where competition leaves their surgeons relatively idle.

For example, Brockton Hospital, south of Boston's powerful hospital cluster, was recently denied permission to conduct certain heart procedures by state officials, who felt the midsize facility would not have enough patient volume to guarantee safety.

Brockton's cardiology chief, Dr. Burton Polansky, calls the decision "tragic," and said patients should consider other factors in addition to volume: "One issue is the amount of training a surgeon has. If you have a reasonable amount of training, then a smaller patient volume number is not as important."

Despite the growing data supporting high patient volume as a quality measure, Polansky said, "It remains to be seen if consumers will discriminate," noting many patients follow the advice of primary care doctors, who often send business to surgeons they know personally.

But consumer pressure is at the heart of the new research: Much of it was conducted in the last four years, prompted in large part by big corporations seeking ways to bring quality control to the medical care consuming an ever-increasing portion of their budgets. Many of the studies can be found on the federal government-sponsored Institute of Medicine Website (www.iom.edu), while a consortium of businesses, called the Leapfrog Group, also maintains an up-to-date Website (www.leapfroggroup.org) of patient volume statistics.

The results remain controversial, with some surgeons convinced measuring patient volume alone is too crude a measure to grade surgeons. But increasingly, the profession admits constant repetition is key to mastering complex surgeries, in which tiny slips can sever veins, damage nerves, and kill patients.

"The more often I do a procedure, the more I fall into a standard routine," said Mackey, a vascular surgeon who performs frequent carotid endarterectomies, delicate procedures that clear a key artery of blockages. "Then, if I encounter something out of the ordinary, I'm quicker to recognize it and correct it."

This week, Mackey is visiting Western Massachusetts hospitals to discuss the link between high volume and success in carotid endarterectomies, which he calls "a hot, hot topic." These surgeons must make incisions in the neck, then slice open the crucial carotid artery and scrape away fat and cholesterol build-up. Imprecision could hinder blood flow to the brain, causing strokes and possibly death.

A December study in the Journal of the American College of Surgeons found that frequent performance of this procedure led to better outcomes. The patients of high-volume surgeons died in 0.4 percent of operations and had strokes, the most serious complication, in 1.1 percent. Average-volume surgeons lost 0.6 percent of their patients, while 1.6 percent suffered strokes. And 1.1 percent of patients who went to low-volume surgeons died, almost triple the rate of high-volume surgeons. Two percent of them suffered strokes, double the high-volume surgeons' rate.

"I think it's simply that practice makes perfect. The more you do something, the more you develop a routine," said Mackey.

Evidence of the pattern has been mounting in other life-or-death procedures, and in some instances the data are striking. During pancreatic cancer surgery, 17 in 100 patients die at low-volume hospitals, compared to only three in 100 at their high-volume counterparts. A similarly high gap occurs in esophageal cancer surgery.

Though some of the studies focused on hospital volume, rather than individual surgeons, specialists said they reinforced the surgeon data because high-volume hospitals are almost always staffed exclusively with high-volume surgeons, with low-volume hospitals far more likely to use low-volume surgeons.

In a study released last week, researchers found the volume pattern held for radical prostatectomies, the most common US treatment for localized prostate cancer, which afflicts 333,000 American men annually. Low-volume surgeons had twice the rate of complications, which include impotence and incontinence, and their patients were hospital-bound for an extra day, compared with high-volume surgeons' patients.

"It's the type of an operation that requires a certain skill. If you really practice, you can get better," said the study's author, Dr. Mark S. Litwin, a University of California at Los Angeles urology professor.

High volume in Litwin's study meant 40 or more procedures annually. The urology chief at Brigham and Women's Hospital, Dr. Jerome P. Richie, performs the surgery up to 200 times a year, four times a week on average.

Richie notes that radical prostatectomy methods have changed drastically in the last 15 years. Frequent practice, he said, was necessary to master the precarious procedure, which involves cutting deep into the pelvis where thick veins weave around the prostate.

"How can I put this delicately?" he said. "I don't want to sound high-handed, but volume matters . . . I would recommend that patients seek surgeons that do at least 50 to 100 cases a year."

After all, said Richie, "they are placing their trust in the hands of someone else."

Dr. Colin Begg, epidemiology chairman at New York City's Memorial Sloan-Kettering Cancer Center, has conducted several of the studies establishing the high-volume pattern, and though his work focuses on cancer, he strongly suspects his results can be applied to many complex surgeries.

Begg said, however, the pattern probably does not hold for less complex surgeries. It did not turn up, for example, in studies of hip fracture repair and knee replacement, considered less technical than procedures on tumors or delicate organs.